Simultaneous Recording of NMR Signals from Nuclei with Different Gyromagnetic Ratios Using Undersampling Technique

Abstract

The article describes experiments on the simultaneous recording nuclear magnetic resonance signals from two nuclei with different gyromagnetic ratios—¹H and ¹⁹F, ¹³C and ²³Na. It is shown that large frequency detunings or/and low sampling rates are not an obstacle to their realization even in a relatively weak (0.5 T) field. We use undersampling technique when registering the response of the spin system. In this case, the sampling frequency is much less than the distance between the Larmor frequencies for the indicated nuclear pairs. It gives the effect of multiple aliasing. Fourier processing of the response produces a spectrum consisting of two subspectra, each of which corresponds to specific nucleus of the investigated pair. The subordination of the spectral peaks in each subspectrum is the same as the spectrum obtained by the usual way. Two variants of the radio-frequency excitation of the spin system (single and double pulse) are considered. A formula for calculating the excitation frequency and sampling rate, which ensures a rational distribution of the lines in the hybrid spectrum, is proposed.